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  • QDs Boost Protein Pinpointing in Cancer Cells
Mar 2013
SEATTLE, March 20, 2013 — Understanding a single cell at its molecular level could better aid in the diagnosis and treatment of cancer. The development of a quantum dot color-coding method that illuminates 100 biomarkers in a single cell could do just that, boosting the ability to pinpoint proteins in cancer cells.

The technique, developed by researchers at the University of Washington, provides a tenfold increase from the current research standard, analyzing the color patterns of individual cells from cultures or tissue biopsies to determine why a cell will or will not become cancerous.

“Discovering this process is an unprecedented breakthrough for the field,” said Xiaohu Gao, an associate professor of bioengineering. “This technology opens up exciting opportunities for single-cell analysis and clinical diagnosis.”

A cell specimen used for two rounds of testing in the University of Washington experiment. In the top panel, two biomarkers are stained green and red, and in the bottom, after the sample has been regenerated, the same biomarkers are stained red and green. This shows that the same tissue can be used for multiple rounds of testing without degrading the tissue sample. Courtesy of Xiaohu Gao, University of Washington.

The research builds on current methods that use a smaller array of colors to point out a cell’s biomarkers — characteristics that indicate a special, and potentially abnormal or diseased, cell. Ideally, scientists would be able to test for a large number of biomarkers, then use the patterns that emerge from those tests to understand a cell’s properties.

The UW scientists devised a cycle technique, making it possible to test for up to 100 biomarkers in a single cell using quantum dots. Cyclical testing — a method that essentially reuses the same tissue sample to test for biomarkers in groups of 10 in each round — had not been done before. 

“Proteins are the building blocks for cell function and cell behavior, but their makeup in a cell is highly complex,” Gao said. “You need to look at a number of indicators [biomarkers] to know what’s going on.”

Xiaohu Gao, left, and doctoral student Pavel Zrazhevskiy in a University of Washington bioengineering lab. Courtesy of Scott Manthey.

Gao and colleagues purchased antibodies that bind with the specific biomarkers they wanted to test for in a cell, then paired them with quantum dots in a fluid solution. This was injected into a tissue sample and observed under a microscope for the presence of fluorescent colors in the cell. If particular quantum dot colors in the tissue sample can be seen, they know the corresponding biomarker is present in the cell.

After one cycle was completed, Gao and bioengineering doctoral student Pavel Zrazhevskiy injected a low-pH fluid into the cell tissue to neutralize the color fluorescence, essentially wiping the sample clean for the next round. After 10 cycles, Gao observed that the tissue sample did not degrade.

The cyclical process developed in the University of Washington study. In step one, the colored balls representing quantum dots of different colors are used to label biomarkers in cell and tissue samples. Step two shows how each biomarker can be isolated and separated into distinct images for analysis. Step three illustrates how the tissue sample is flushed clean between rounds to begin biomarker testing again. Courtesy of Xiaohu Gao, University of Washington.

The relatively low-cost and simple process could be automated, Gao said. He envisions a chamber to hold the tissue sample and wire-thin pumps to inject and vacuum out fluid between cycles. A microscope underneath the chamber would take photos during each stage. All images would be quantified on a computer, where scientists and physicians could look at the intensity and prevalence of colors.

“The technology is ready,” Gao said. “Now that it’s developed, we’re ready for clinical impacts, particularly in the fields of systems biology, oncology and pathology.”

The research, funded by the National Institutes of Health, the National Science Foundation, the Department of Defense, the Wallace H. Coulter Foundation and the UW’s Department of Bioengineering, appeared in Nature Communications (doi: 10.1038/ncomms2635). 

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quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.  
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